How do I set weight painting brushes to limit total vertex weight to 1?
The auto-normalise setting in the brush menu will make it so the total weights on any vertex that you paint are adjusted to sum to 1. This has bee in blender for a long time, see https://docs.blender.org/manual/en/latest/sculpt_paint/painting/weight_paint/tools.html.

The menu options is here in 2.8: